we could find out the reflection of the light quanta on the [thermometer], and the path of the remaining light quanta into the eye of the observer, their refraction in the eye lens, and the formation of an image on the retina, and then we would say: this image is registered by the retina of the observer.

And were our physiological knowledge more precise than it is today, we could go still further, tracing the chemical reactions which produce the impression of this image on the retina, in the optic nerve tract and in the brain, and then in the end say: these chemical changes of his brain cells are perceived by the observer. But in any case, no matter how far we calculate -- to the mercury vessel, to the scale of the thermometer, to the retina, or into the brain, at some time we must say: and this is perceived by the observer. That is, we must always divide the world into two parts, the one being the observed system, the other the observer.

Information Can Only Be Recorded If Compensating Entropy Is Transferred Away

If entropy cannot be carried away, the information is lost.

When the photon irreversibly blackens a spot on the photographic plate, this is the "cut." Information becomes available for observation at a later time.

The "cut" is also the transition from the quantum world to the "adequately"
classical world that decoherence theorists (Zeh, Zurek) are looking for.